Ball grid array rework

ABSTRACT

Embodiments of the invention relates to a method and apparatus for rework of a BGA package. Memory shape material is placed adjacent to a plurality of solder joints of the package. Stimulation is applied to the material, with the stimulation causing the material to change from a non-stimulated shape to a stimulated shape. This stimulation causes an expansion of the material. As the material expands, it exerts a tensile force on the BGA package and an adjacently positioned carrier, causing a separation of the two components, while mitigating collateral heat of adjacently positioned components.

BACKGROUND

The present invention relates to rework for a ball grid array package,including removal of the ball grid array package from an associatedprinted circuit board or carrier. More specifically, the inventionrelates to an expansion material and control of the material in a mannerthat applies an expansion force to adjacently positioned solder joints.

Computer systems are generally configured with a memory module(s) andintegrated circuits in communication with a printed circuit board (PCB).A ball grid array package (BGA) is a type of surface-mount packagingused for integrated circuits. BGA packages are used to permanently mountdevices such as microprocessors. The BGA package uses a grid of solderballs as its connectors to a printed circuit board (PCB) or carrier.Rework pertains to repair or refinishing a PCB assembly. The aspect ofrework generally includes uncoupling the package or other electroniccomponents from the substrate, and in one embodiment re-solderingcomponents to the substrate.

BRIEF SUMMARY

The invention comprises an apparatus for a rework process that employslocalized heating for expanding solder joints between the BGA and thePCB.

A BGA package is assembled on to a printed circuit board with anexpansion material. Configuration of the package includes interstitialplacement of the material within a matrix of solder joints. A tensileforce is applied between a ball grid array (BGA) package and the printedcircuit board through delivery of electrical current to the material. Inone embodiment, the application of the force is controlled. The currentcreates a localized heating of the expansion material, and the heatedmaterial applies an expansion force to the solder joints. This expansionforce separates the BGA from the printed circuit board.

Other features and advantages of this invention will become apparentfrom the following detailed description of the presently preferredembodiment(s) of the invention, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The drawings referenced herein form a part of the specification.Features shown in the drawings are meant as illustrative of only someembodiments of the invention, and not of all embodiments of theinvention unless otherwise explicitly indicated.

FIG. 1 depicts a perspective view of a ball grid array package with anexpansion material.

FIG. 2 depicts a cross sectional view of the BGA package incommunication with a PCB prior to application of a stimulus.

FIG. 3 depicts a cross sectional view illustrating expansion of thesolder joints following application of a stimulus to the associatedexpansion material.

FIG. 4 depicts a cross sectional view illustrating further expansion ofthe material following application of the stimulus.

FIG. 5 depicts a flow chart illustrating a process for decoupling anassembled BGA package and the PCB.

FIG. 6 depicts a block diagram of a system with a computer incommunication with PCB.

FIG. 7 depicts a block diagram of a computing environment according toan embodiment of the present invention.

DETAILED DESCRIPTION

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,may be arranged and designed in a wide variety of differentconfigurations. Thus, the following detailed description of theembodiments of the apparatus, system, and method of the presentinvention, as presented in the Figures, is not intended to limit thescope of the invention, as claimed, but is merely representative ofselected embodiments of the invention.

Reference throughout this specification to “a select embodiment,” “oneembodiment,” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “a select embodiment,” “in one embodiment,”or “in an embodiment” in various places throughout this specificationare not necessarily referring to the same embodiment.

The illustrated embodiments of the invention will be best understood byreference to the drawings, wherein like parts are designated by likenumerals throughout. The following description is intended only by wayof example, and simply illustrates certain selected embodiments ofdevices, systems, and processes that are consistent with the inventionas claimed herein.

An apparatus and method for a rework process creating localizedstimulation for localized heating and expansion of solder joints betweena BGA and a PCB or an alternate substrate is described in detail below.The apparatus and method employs an expansion material in communicationwith the BGA package and the PCB. More specifically, the expansionmaterial is interstitially placed within a matrix of BGA solder joints.The material is comprised of a memory shape alloy, or in one embodiment,a high z-axis coefficient of thermal expansion material. When subject tostimulation, such as heating, the material expands, and this expansionapplies an expansion force to both the PCB and the BGA package. In oneembodiment, the heated material has an exothermic reaction, and the heatsoftens the adjacently positioned solder joints. Accordingly,application of heat to the material both expands and softens the solderjoints, thereby facilitating separation of the BGA from the PCB.

Referring now to FIG. 1, a perspective view (100) of a ball grid arraypackage (rendered transparent) is shown assembled on to a PCB orsubstrate with an expansion material situated interstitially between thesolder joints. As shown, the BGA package is shown with a substrate (110)and a matrix of solder balls (120). An expansion material (130) isplaced within the matrix (120). In one embodiment, the matrix (120)includes a plurality of rows and columns. The material (130) is shownplaced in each adjacently positioned row in the matrix (120). In oneembodiment, the material (130) may be placed in alternative rows of thematrix, and should not be limited to adjacently positioned rows. Thematerial (130) is comprised of a height and width that enables it to bereceived within the matrix. In one embodiment, the width of the materialis limited to the width between adjacently positioned solder balls.Similarly, in one embodiment, the height of the material is limited tothe height of the solder balls from the base of the substrate (110) tothe top surface of the solder ball (122). The BGA package may bepre-configured with the material within the matrix of solder joints, orin one embodiment, the material may be threaded or otherwise placedadjacent to the solder joints. Accordingly, the configuration of thematerial is limited by the configuration of the matrix, and specificallyby the dimensions and positioning of the solder balls that comprise thematrix.

The BGA package shown in FIG. 1 is an illustration of the transparentball grid array package assembled on to the PCB or substrate. Referringto FIG. 2, a cross sectional view (200) of the BGA package incommunication with a PCB prior to application of force. As shown, theBGA package (210) is in communication with the PCB (230) through anarray of solder balls (220). A gap (250), also referred to herein as afirst gap, represents the spacing between the BGA package (210) and thePCB (230) formed by the connection of the PCB (230) and the BGA package(210) via one or more solder joints (220), also referred to herein as asolder ball connection. Specifically, the solder joints (220) hold thePCB (230) and BGA (210) in a fixed relationship. In one embodiment, theconnection formed by the solder balls is referred to as a solder joint.Expansion material (not shown) is positioned between adjacentlypositioned solder joints. Specifically, the expansion material isarranged in parallel on both sides of the solder joint in the gap (250).Accordingly, the expansion material occupies vacant space formed betweenadjacently positioned solder joints.

The expansion material shown in FIGS. 1 and 2, represents the materialat a rest state prior to expansion of the material and/or expansion ofthe adjacently positioned solder joints. The material is configured tochange shape in response to a stimulus. Referring to FIG. 3, a crosssectional view (300) is provided illustrating expansion of the solderjoints following application of a stimulus to the associated expansionmaterial. As shown, the BGA package (310) is in communication with thePCB (330) through an array of solder balls (320). A gap (350), alsoreferred to herein as a second gap, represents the spacing between theBGA package (310) and the PCB (330) formed by the connection of the PCB(330) and the BGA package (310) via one or more solder joints (320),also referred to herein as a solder ball connection. Expansion material(340) is shown between adjacently positioned solder joints.Specifically, the expansion material (340) is arranged in parallel onboth sides of the solder joint. As shown herein, the expansion material(340) has an expanded form and elongated shape following receipt of astimulus and in comparison to the material (240) shown in FIG. 2 priorto receipt of a stimulus. In addition, the second gap (350) is shownlarger than the first gap (250), as a result of the change in size andshape of the expansion material (140). As shown, the size and shape ofthe expansion material (340) changes and elongates in response to thestimulus. In one embodiment, the size and shape of the solder joints(320) also changes in response to the changes experienced by thematerial (340). As shown herein, in one embodiment, the solder joints(320) elongate in conjunction with, or in response to, the elongation ofthe material (340). Accordingly, application of stimulus to theexpansion material (340) increases the size of the second gap (350)representing the space between the BGA package (310) and the PCB (330).

The focus of the expansion material is to facilitate rework of the BGApackage. Rework may be required for a plurality of reasons, includingreplacement, upgrade, etc., of a component. In FIG. 3, the expansion ofthe material in conjunction with expansion of the solder joints isshown. Referring to FIG. 4, a cross sectional view (400) is providedillustrating further expansion of the material following application ofthe stimulus. The BGA package (410) is shown with limited communicationwith the PCB (430). More specifically, a gap (450) represents spacingbetween the BGA package (410) and the PCB (430). The gap (450) is alsoreferred to herein as a third gap. Responsive to the expansion of thematerial (440), the solder joints (420) are severed. As shown, a firstportion of the solder joint (422) is in communication with the BGApackage (410) and a second portion of the solder joint (424) is incommunication with the PCB (430). In one embodiment, the deformed solderjoints remain in communication with the PCB (430) and are removed fromthe BGA package (410). The severing of the solder joint (420) is inresponse to expansion of the material (440). In one embodiment, thematerial (440) remains contiguous, while the solder joints are sheared.The expansion of the material (440) applies a high out of plane force onthe PCB (430) and on the bottom of the package (410). Accordingly, aresulting effect of the material expansion severs the solder joints.

Referring to FIG. 5, a flow chart (500) is provided illustrating aprocess decoupling the BGA package and the PCB. As shown, a material isfed through a matrix of solder balls on the BGA package (502). In oneembodiment, the matrix includes a plurality of rows and columns, and thematerial is arranged in parallel across the rows or across the columns.Similarly, in one embodiment, the material is placed in each adjacentlypositioned row or column, or in another embodiment, the material isplaced in selected rows or columns within the matrix. In one embodiment,the material placed in the matrix includes a memory shape alloy.Following the material placement, an electric current is driven throughthe material (504). The current delivers heat to the material andpromotes a high z-axis expansion of the material (506). In oneembodiment, the material has an original expanded shape and is placed inthe matrix in a reduced shape. When subject to heating or in receipt ofelectrical current, the material transforms from the reduced shape tothe original expanded shape. In one embodiment, delivery of electricity,referred to herein as a compression mode, is controllable with theamount of electricity proportional to the expansion of the material.Similarly, in one embodiment, external heating may be applied to thesolder joints (508). In one embodiment, the external heating isdelivered from a hot air rework nozzle. Similarly, in one embodiment,the material receives electrical current concurrent with the externalheating directed to the solder joints. Delivery of the current and theheat may be concurrent or sequential. The expansion force from thematerial severs the solder joints (510), and the PCB is then separatedfrom the BGA package (512). Accordingly, delivery of current to thematerial transforms the material into an expanded shape, forcing the PCBand the BGA package to separate.

As shown in FIGS. 1-5, displacement growth between the BGA package andthe PCB, also referred to as the carrier, is driven by expansion of thematerial and solder joint deformation due to displacement. In oneembodiment, neither the displacement nor the solder joint deformation isuniform. However, the memory shape alloy material supports direct heatdelivery to a specified location and mitigates collateral heat ofadjacently positioned components. Accordingly, the heat delivery isdirect and specific.

As shown and described herein, the memory shaped alloy material isplaced within the matrix of the solder joints in a reduced form. Whensubject to heat, the material transform into an expanded shape.Expansion of the material is limited with respect to the configurationof the carrier. In one embodiment, the maximum z-axis expansion is 42.5microns. To ensure expansion in the direction of the solder joint, theseparation force may be tuned through use of anisotropic expansionmaterials. In one embodiment, the anisotropic expansion materials may bein a rectangular form with an elongated axis, such as a ribbonstructure. Accordingly, selection of materials may be employed withrespect to the structure of the carrier and/or the desired expansion forrework.

The rework illustrated and described herein is with respect to a BGApackage and a carrier. In one embodiment, the expansion material may beused to separate one or more die in a multi-die stacked package. Thememory shape alloy material enables the separation while mitigatingcollateral reflow from any adjacently positioned components.Accordingly, the application of the memory shape alloy material may beexpanded to various configurations within a carrier and associatedpackages and die.

The BGA rework may be automated through a series of tools and associatedcomputer readable and executable instructions. Referring to FIG. 6, asystem is provided with a computer in communication with PCB. Thecomputer (610) is provided with a processing unit (612) operably coupledto memory (614) across a bus (616). One or more tools are shown tofacilitate expansion of the memory shaped alloy material placed adjacentto the solder joints of the BGA package. The tools include an applicator(624) to deliver the electrical current to the material, and a regulator(626) to control the level of current being delivered. In oneembodiment, one or more computer readable instructions are processed tocontrol the delivery of current to the material. Similarly, in oneembodiment, the level of current delivered to the material is directlyor indirectly proportional to the tensile force between the BGA packageand the PCB, and by controlling the current, the regulator (626)controls the application of force. Rework may be directed to a specificBGA package, a multi-stack die, or in one embodiment, a combination oftwo or more packages or die. The applicator (624) and regulator (626)are employed to direct the rework to a designated location andassociated material.

The tools shown in FIG. 6 may be implemented in programmable hardwaredevices such as field programmable gate arrays, programmable arraylogic, programmable logic devices, or the like. The tool may also beimplemented in software for execution by various types of processors. Anidentified functional unit of executable code may, for instance,comprise one or more physical or logical blocks of computer instructionswhich may, for instance, be organized as an object, procedure, function,or other construct. Nevertheless, the executable of the tool need not bephysically located together, but may comprise disparate instructionsstored in different locations which, when joined logically together,comprise the tool and achieve the stated purpose of the tool.

Indeed, executable code could be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different applications, and across several memorydevices. Similarly, operational data may be identified and illustratedherein within the tool, and may be embodied in any suitable form andorganized within any suitable type of data structure. The operationaldata may be collected as a single data set, or may be distributed overdifferent locations including over different storage devices, and mayexist, at least partially, as electronic signals on a system or network.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of agents, to provide a thorough understanding of embodimentsof the invention. One skilled in the relevant art will recognize,however, that the invention can be practiced without one or more of thespecific details, or with other methods, components, materials, etc. Inother instances, well-known structures, materials, or operations are notshown or described in detail to avoid obscuring aspects of theinvention.

Referring now to the block diagram of FIG. 7, additional details are nowdescribed with respect to implementing an embodiment of the presentinvention. The computer system includes one or more processors, such asa processor (702). The processor (702) is connected to a communicationinfrastructure (704) (e.g., a communications bus, cross-over bar, ornetwork).

The computer system can include a display interface (706) that forwardsgraphics, text, and other data from the communication infrastructure(704) (or from a frame buffer not shown) for display on a display unit(708). The computer system also includes a main memory (710), preferablyrandom access memory (RAM), and may also include a secondary memory(712). The secondary memory (712) may include, for example, a hard diskdrive (714) and/or a removable storage drive (716), representing, forexample, a floppy disk drive, a magnetic tape drive, or an optical diskdrive. The removable storage drive (716) reads from and/or writes to aremovable storage unit (718) in a manner well known to those havingordinary skill in the art. Removable storage unit (718) represents, forexample, a floppy disk, a compact disc, a magnetic tape, or an opticaldisk, etc., which is read by and written to by removable storage drive(716). As will be appreciated, the removable storage unit (718) includesa computer readable medium having stored therein computer softwareand/or data.

In alternative embodiments, the secondary memory (712) may include othersimilar means for allowing computer programs or other instructions to beloaded into the computer system. Such means may include, for example, aremovable storage unit (720) and an interface (722). Examples of suchmeans may include a program package and package interface (such as thatfound in video game devices), a removable memory chip (such as an EPROM,or PROM) and associated socket, and other removable storage units (720)and interfaces (722) which allow software and data to be transferredfrom the removable storage unit (720) to the computer system.

The computer system may also include a communications interface (724).Communications interface (724) allows software and data to betransferred between the computer system and external devices. Examplesof communications interface (724) may include a modem, a networkinterface (such as an Ethernet card), a communications port, or a PCMCIAslot and card, etc. Software and data transferred via communicationsinterface (724) is in the form of signals which may be, for example,electronic, electromagnetic, optical, or other signals capable of beingreceived by communications interface (724). These signals are providedto communications interface (724) via a communications path (i.e.,channel) (726). This communications path (726) carries signals and maybe implemented using wire or cable, fiber optics, a phone line, acellular phone link, a radio frequency (RF) link, and/or othercommunication channels.

In this document, the terms “computer program medium,” “computer usablemedium,” and “computer readable medium” are used to generally refer tomedia such as main memory (710) and secondary memory (712), removablestorage drive (716), and a hard disk installed in hard disk drive (714).

Computer programs (also called computer control logic) are stored inmain memory (710) and/or secondary memory (712). Computer programs mayalso be received via a communication interface (724). Such computerprograms, when run, enable the computer system to perform the featuresof the present invention as discussed herein. In particular, thecomputer programs, when run, enable the processor (702) to perform thefeatures of the computer system. Accordingly, such computer programsrepresent controllers of the computer system.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method, or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.), or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module,” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including, but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++, or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer, or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider.

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowcharts and/or block diagram block(s).

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the functions/acts specified in the flowcharts and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus, or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowcharts and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowcharts or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblocks may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustrations,and combinations of blocks in the block diagrams and/or flowchartillustrations, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated. Employment of the memory shaped materialfor the rework supports direct application of the rework to a specificcomponent. Accordingly, the placement and arrangement of the shapechanging material enables and supports rework to a direct location,while mitigating collateral heat to adjacently positioned components.

ALTERNATIVE EMBODIMENT

It will be appreciated that, although specific embodiments of theinvention have been described herein for purposes of illustration,various modifications may be made without departing from the spirit andscope of the invention. In one embodiment, the expansion material may bein the form of a wire that is fed through the matrix of solder balls.The material is shown to be placed in a parallel or relatively parallelarrangement within the matrix. In one embodiment, the material may beplaced in the matrix in a non-parallel arrangement. Accordingly, thescope of protection of this invention is limited only by the followingclaims and their equivalents.

We claim:
 1. An apparatus comprising: a ball grid array (BGA) package assembled on to a printed circuit board; an expansion material placed between the BGA package and the printed circuit board, including interstitial placement of the material within a matrix of solder joints between the BGA package and the printed circuit board; an applicator in communication with the material, the applicator to apply a tensile force between a ball grid array (BGA) package and the printed circuit board, including delivery of electric current to the expansion material, wherein the application of the tensile force is controlled by a regulator in communication with the applicator; a localized heating of the expansion material created from the current; an expansion force applied to the solder joints from the heated material, the expansion force including separation of the BGA from the printed circuit board.
 2. The apparatus of claim 1, further comprising the expansion force to elongate the solder joints into two parts, including a first part to remain in communication with the BGA package and a second part to remain in communication with the printed circuit board.
 3. The apparatus of claim 1, wherein the expansion material is selected from the group consisting of: a memory shape alloy and a high z-axis coefficient of thermal expansion material.
 4. The apparatus of claim 1, further comprising an alignment of the material in parallel across the matrix, including parallel placement of the material positioned between BGA package solder joints.
 5. The apparatus of claim 1, further comprising the application to deliver heat from an external source to the solder joints concurrent with delivery of the electric current to the material. 